A semiconductor device is employable for a compact and light-weight sensor system that is free of the need for battery replacement. The semiconductor device has a sensor chip (SCHIP1) comprising sensors (TD1, AS1, PD1, GS1), an A/D conversion circuit (AD1), a microprocessor (CPU1), a memory (MEM1), a transmission circuit (RF1), and a power generation circuit (CM1). The sensors, the A/D conversion circuit, the microprocessor, the memory, and the transmission circuit are formed on one side (SIDE1) of a substrate, while the power generation unit is formed on the other side (SIDE2) of the substrate.